AG 1997 09 15 - Laserfiche WebLink

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Proposed Radio Tower Page 5 Cabarrus County Sheriffs Dept. Footings bearing on the residual soil at a depth of 5 f~ or greater may be designed for a maximum allowable net bearing pressure of 3000 psf. Individual footings should have a minimum widths of 24 inches. This minimum width provides a margin of safety against a local or puhching shear failure of the foundation soils. Footings should bear at least 18 inches below final exterior grade to provide frost protection and protective embedment. Individual footings should bear entirely in either compacted fill or residual soil over their entire bearing area. In order to verify that the soils encountered in the bottoms of undercutting excavations and/or footing excavations are do not vary significantly from those encountered in the soil test borings, the foundation excavations should be examined and test. ed with a dynamic hand penetrometer by an experienced engineering technician working under the direct supervision of the geotechnical engineer. Exposure to the environment may weaken the soils at the footing bearing level if the foundation excavations remain open for long periods of time. Therefore, I recommend that all footing excavations be extended to final grade and the footings constructed as soon as possible to minimize the potential damage to bearing soils. The foundation bearing area should be level or suitably benched and be free of loose soil, ponded water and debris. Foundation concrete should not be placed on soils that have been disturbed by seepage. If the bearing soils are softened by surface water intrusion or exposure, the softened soils must be removed from the foundation excavation bottom immediately prior to placement of concrete. If the excavation must remain open overnight or if rainfall becomes imminent while the bearing soils are exposed, I recommend that a 2 to 4-inch thick "mud-mat" of "lean" (2000 psi) concrete be placed on the bearing soils before the placement of reinforcing steel. $it¢ Preparation and Grading Due to the nature of this project, we have omitted our typical recommendations for pavement and slab subgrades. We will include them under separate cover if the need arises. Qualification of Report My evaluation of foundation support conditions has been based on my understanding of the site and project information and the data obtained in my exploration. The general subsurface conditions utilized in my foundation evaluation have been based on interpolation of subsurface data between the borings. In evaluating the boring data, I have examined previous correlation between penetration resistance and foundation bearing pressures observed in soil conditions similar to those at your site. File: 97-026R.sam